The invention pertains to a hydraulic binding agent based on cement clinker ground without addition of gypsum and provides a composition of a binding agent with controlled beginning of setting, where high values of strength increase from the beginning of setting. The invention further pertains to a method of preparation of said binding agent and of other products from it.
A cement clinker is obtained by calcination of the ground mixture of limestone and clays to a temperature of about 1400.degree. C., when the mixture sinters. The most common type of cement is portland cement, which is obtained by grinding the cement clinker with the addition of gypsum as a regulator of setting. A binding agent, obtained by grinding a cement clinker without gypsum, sets instantaneously and is unsuitable for current applications. For this reason the recent binding agents based on silicates always contain gypsum as an additive added predominently during the cement grinding. Gypsum is considered a very common additive in portland cement. Other additives, particularly various plasticizers, added into portland cement are considered only in combination with gypsum.
P. A. Rebinder et al. (Doklady Akad. Nauk SSSR, 117, 1034-1036 (1956)) proved that the mixture of calcium lignosulfonate with K.sub.2 CO.sub.3 causes retardation of the beginning of setting of cement pastes with the subsequent considerable acceleration of the hydration process. This effect was found both with a finely ground clinker of specific surface area 450 m.sup.2 /kg prepared without gypsum and with portland cement containing gypsum. S. Brunauer described in U.S. Pat. No. 3,689,294 a binding agent, which attains much higher strength than common portland cements. He concluded that high strengths of setting cement pastes, mortars and concretes based on a ground cement clinker may be achieved in the absence of gypsum but in the presence of other setting regulators. The above patent disclosed the method of preparation of an expansible cement binding agent by grinding a portland clinker with at least 0.002 weight parts of an auxiliary grinding agent to the cement with the specific surface area ranging from 600 to 900 m.sup.2 /kg and mixing the ground cement with at least 0.0025 weight parts of alkaline or alkaline earth lignosulfonate or sulfonated lignin and with 0.20 to 0.28 weight parts of water containing dissolved at least 0.0025 weight parts of alkaline carbonate, calculated on one part of ground cement. L. Stryker concluded in U.S. Pat. No. 3,959,004 that alkaline hydrogencarbonate can be used in gypsum-free cements instead of alkaline carbonate. He described a method for the preparation of a gypsum-free loosely running cement paste of low porosity manufactured by grinding the hydraulic clinker to a fineness of 350 to 900 m.sup.2 /kg with 0.1 to 1% alkaline or alkaline earth lignosulfonate or sulfonated lignin in combination with 20 to 40% water containing 0.1 to 2% alkaline hydrogencarbonate and the subsequent mixing of all components, where all percent values are related to dry cement.
Ball et al. described in U.S. Pat. No. 3,960,582 the composition of a mixture for the preparation of cement paste in such a way, also that portland cement may be used instead of the clinker ground without gypsum and, further, alkaline lignin may be employed in addition to lignosulfonates and sulfonated lignin. The same authors described in U.S. Pat. No. 4,032,353 the composition of a mixture of low porosity consisting of aggregates, a hydraulic cement without gypsum of the specific surface area above 200 m.sup.2 /kg, alkaline hydrogencarbonate in the amount of at least 0.1% related to the dry cement, and a lignin derivative in the amount at least 1% related to the dry cement. The water-to-cement ratio ranged between 0.4 and 0.15.
The composition of gypsum-free very rapidly setting binding agent, based on the cement ground to the specific surface area ranging from 300 to 700 m.sup.2 /kg and containing acidic salts, as hydrogencarbonates, hydrogensulfates, alkaline hydrogensulfites as well as salts of phosphorus-free organic acids, is known from U.S. Pat. No. 4,066,469. The additives are present in the mixture in the amount 0.1 to 10% calculated on the weight of ground cement.
The beginning of setting of pastes, mortars and concrete mixtures depends usually on the cement composition, the amount of water used and the temperature of the processed mixture and of the environment, particularly of the atmosphere. The time for which it is possible to keep the paste, mortar or concrete mixture in a processable state, i.e. the period of time from the beginning of its setting during which some technical procedures should be made, e.g. before consolidation of concrete, is also of great importance in this case. Such technical procedures are above all transportation and storage of the mixture. If handling of a concrete mixture requires relatively longer time or if the operation proceeds at unsuitably high temperature, the course of initial hydrogen has to be slowed down by at least 6% of the period of time. This may be achieved by admixing suitable chemical compounds.
It has been found during investigation and testing of various additives to binding agents, that additives which retard the setting should meet the following conditions: they should slow down the hardening of pastes, mortars and concretes without negative effect on their properties, such as compression strength, tensile strength and bending strength; they should also favourably affect the moduli of elasticity and deformability, volume changes, resistance to unsuitably low temperature and resistance to efflorescence. They should also act as a suitable plasticizer of the mixture. The additives to hydraulic binding agents known till now meet only some of the above requirements and are responsible for the search for new additives or their new combinations with better effects to help in the preparation of hydraulic binding agents with broader applications.
This invention also pertains to a method for the preparation of rapidly binding high-strength cement binding agent for the manufacturing of mortars, pastes and concretes, which setting is sufficiently fast but controllable and which imparts high strength to the set masses from the beginning of setting. U.S. Pat. No. 3,689,294 revealed the preparation of loosely running expansible cement paste by grinding the portland cement clinker with an auxiliary grinding agent to the specific surface area 600-900 m.sup.2 /kg and the subsequent mixing of the ground clinker with alkaline or alkaline-earth salts of lignosulfonate or sulfonated lignin, where the cement prepared in this way is mixed with formation water containing alkaline carbonate.
Another modification of the preparation of cement pastes is known from U.S. Pat. No. 3,960,582 and consists in the grinding of a portland cement clinker with alkaline hydrogencarbonate without the addition of gypsum, and optionally also with alkaline or alkaline-earth lignosulfonate or a salt of sulfonated lignin, followed by mixing the cement prepared in this way with formation water.
U.S. Pat. No. 4,032,353 protects the manufacturing of loosely running concretes based on mixing a clinker or hydraulic cement, ground to the specific surface area larger than 200 m.sup.2 /kg, with alkaline hydrogencarbonate and the subsequent preparation of a paste by its mixing with formation water which contains the dissolved lignin derivative.
The above mentioned procedures accelerate the setting of resulting concretes and mortars, but the initial onset of strength of setting concretes and mortars, but the initial onset of strength of setting concretes and mortars is slow and handling of articles prepared in this way is possible only after attaining a reasonable limit of strength. This pause in technology deteriorates the rhythm of production.